1. Field of the invention
This invention relates generally to door locking systems, and more particularly, to a locking assembly for use in slidable doors and the like.
2. Discussion of the prior art
Sliding doors and windows are finding wide current architectural usage because they are inexpensive to construct and do not require clearance in the interior of the building. Despite these advantages, they have been an easy point of entry for burglars and other types of criminals. To date, most of the locking mechanisms for sliding glass panels of this type have been primitive and unsatisfactory. Many of these locks can be overcome by simply forcing a pry bar between the door or window and it's casing and applying a moderate amount of force. In view of this well-known weakness, most homeowners adopt the expedient of laying a dowel in the lower track of the sliding panel. While this may discourage the unskilled thief, it is usually not effective against the professional burglar who can often insert a thin bar along the edge of the window and flip the dowel out of the channel. This is especially easy to do if the door has been slightly opened to obtain better ventilation.
Another common security device is a hinged bar across the door. This is attached at one end to the door or window frame while the other end rests in a channel attached to the casing. This bar needs only be lifted from the retaining channel in order to open the door. Once again, enterprising thieves have devised tools and means to accomplish this purpose in a fair number of installations.
Various devices have been proposed in the art for increasing the locking security of a patio door, so that an intruder or other unauthorized person cannot force the door unless he resorts to smashing the entire glass panel. One such prior art locking device is shown in U.S. Pat. No. 4,295,676 which includes a pair of telescoping members that are adjustably interconnected to have either a greater or lesser length. One of the telescoping members attaches to a keeper on the sliding door, and is non-removably retained in the keeper whenever the shorter length is selected so that the door may be ajar, or when the door is locked in the fully closed position. U.S. Pat. No. 3,608,940 discloses a sliding door security lock of telescoping members limited in movement in a contracted direction. One end being attached to the frame of the sliding door itself and the other end being attached to the doorjamb or a second door in the doorjamb. Both attachments are releasable, one by retracting one member when the door is closed and the other by angularly moving the other member when the one member is retracted. The one member is latched by a pivoted coaxial keeper in its telescoping position and the latch is held by the other member when the door is open.
U.S. Pat. No. 4,102,545 discloses a lock assembly which includes a specially configured bracket which is mounted upon the stationary frame assembly of the door unit. The bracket is mounted upon the stationary frame assembly of the door unit. The bracket has an inverted "J" shaped channel and an elongated wall defining a plurality of apertures including one aperture which is positioned to overlie an aperture in the slidable frame of the door when the door is in a closed position and another aperture which is positioned to overlie the aperture in the slidable frame when the door is in a partially opened position. A specially configured locking key is provided with a cylindrical shank having an arcuate locking cam for lockably engaging the inverted "J" shaped channel bracket when the shank is inserted into the aperture in the slidable frame into one of the apertures in the bracket.
U.S. Pat. No. 4,493,501 discloses a toggling pair of bars, one of which is attached to the door frame and the other to the casing so that the bar lies across the fixed pane. The first bar is an inverted channel which encloses a portion of a second preferably solid bar. A pair of longitudinally side by side holes is drilled through both bars in the overlapping portion. The bars are joined in this area by one or more pins inserted through the holes. One hole is located adjacent to the distal end of the solid bar so that it can act as a pivot when the bars are united by a pin passing through this hole. The bars can then toggle to permit the door to be opened. If both holes are pinned or if a single pin is placed so that it passes through the other hole in the solid bar assembly is securely locked.
Other sliding door locking devices are shown in U.S. Pat. Nos. 4,790,157; 4,563,885; 4,763,497; and 4,754,624. Other means which offer a higher degree of security are known, but these are considered by most people to be undesirable from points of complexibility, expense, or appearance. There has been a major unfilled need for a highly effective security device for sliding doors or windows that is simple, moderately priced, and does not detract from the esthetic appearance.